In power electronics, efforts have increasingly been made for a relatively long time to protect the integrated circuits used against overloading and to initiate suitable measures in the case of electrical or thermal overload. For this purpose, the current flow through a corresponding circuit, in particular a power semiconductor device, and/or the temperature thereof is usually detected and compared with predetermined limit values.
Thus, for realizing self-protecting MOS power semiconductor devices, it is known to provide a current sensor and a temperature sensor on the chip. In an embodiment which is likewise known and often put into practice, the current sensor is embodied as a small DMOS transistor that supplies a current proportional to the load current in the power switching device if the voltage values applied to it are the same as those applied to a load DMOS transistor. This small transistor, which is also referred to as a sense DMOS, has an area which is smaller than that of the load DMOS by a factor of 1,000 to 100,000. A current flows through it which is smaller, ideally by the geometrical ratio of the active areas, than the current flowing through the load DMOS and is therefore a measure of the latter current.
In the form of realization of a common-drain technology, the same drain potential and the same gate potential are present at both transistors. The source potential is tapped off suitably at the load DMOS, and the source potential of the sense DMOS is set to the same potential value. The current that flows in this state is then measured. The current serves as an indicator of the load current presently flowing through the load DMOS.
Conventionally, the source potential at the load DMOS is tapped off in various ways.
Thus, it is known to provide a metal tapping at a measuring point at the chip edge.